This invention relates to a thin film semiconductor device that can be produced without using any vacuum apparatus or photolithography, and a process for producing thereof.
Technique for forming TFT (thin film transistor) on a large-area substrate of glass, or the like has been developed, and liquid crystal displays using such TFT as a drive circuit have been commercialized. And, there is desired a process for producing thin film semiconductor devices having good characteristics, TFT in particular, at high yields. A conventional TFT array for a liquid crystal display has been produced by several methods, one example of which will be explained below by reference to drawings.
An ITO film is formed on a glass substrate 22 (vacuum is necessary), the film is selectively etched to form a cumulative capacity electrode 21, and an overcoat 20 of an SiO.sub.2 film is formed (mask is necessary) (FIG. 7).
An ITO film is formed (vacuum is necessary), and a pixel electrode 23 is selectively formed (mask is necessary) (FIG. 8).
Again, an overcoat of an SiO.sub.2 film is formed to form an electrically conductive film (vacuum is necessary), and a TFT gate electrode 24 is selectively formed (mask is necessary) (FIG. 9).
A gate-insulating film, an i-type semiconductor layer 26 and a TFT protective film 27 are formed (vacuum is necessary) (FIG. 10).
The protective film 27 is retained in a region between a TFT source and a drain (FIG. 11).
A contact hole 28 is made in part of the ITO pixel electrode (mask is necessary) (FIG. 12).
An n-type semiconductor layer 38, which is an ohmic layer, is formed (vacuum is necessary), and it is selectively etched except for its TFT portion (mask is necessary) (FIG. 13).
An electrically conductive layer is formed (vacuum is necessary), and there formed selectively are a source 30, a drain electrode wiring 29, etc., (mask is necessary) (FIG. 14).
In the above steps, seven masks are necessary, and many vacuum apparatus are also necessary.
An discussed above, a large vacuum film-forming apparatus and an aligner for photolithography have been conventionally required to commercialize a large-sized liquid crystal display using, as a drive circuit, TFT formed on a large-area substrate of glass, or the like. The limit in increasing the size of a liquid crystal display is defined by these apparatus.